Graphical user interfaces with multi-touch displays may be configured to accept input simultaneously from a plurality of users. Further, each user may interact with one or more user interface elements that are displayed by the multi-touch display. For example, two users may interact with a set of digital images and each user may manipulate a different digital image from the set at the same time. As such, there may be several active user interface elements on the multi-touch display that have the potential to overlap as users manipulate the elements.
Therefore, user interface elements on a graphical user interface are assigned a z-ordering to determine which user interface elements are displayed in front of other elements in the case of overlap. Such z-ordering may affect various functionalities, such as drag-and-drop actions.